AMONG PC gaming’s biggest attractions is modding — where ordinary fans change aspects of a game for fun and then give away the results.

Mods can consist of almost anything, can come from the mind of almost anyone and, as a result, can offer some of the most beautiful, terrifying and downright surreal virtual experiences available anywhere in modern life.

Want to hunt down a fire-breathing Thomas the Tank Engine while riding a horse with photo-realistic genitals and decked out in My ­Little Pony-themed armour? Those are all downloadable mods for high fantasy role-playing game Skyrim.

At their most impressive, sprawling mods can completely transform a title. Such is Diaspora, a four-year transformation of space shooter Freespace 2 into a stunning Battle­star Galactica flight simulator. Such “total conversions” can even spawn entirely new game genres, using the bones of old titles.

It is a chaotic, sprawling scene with a pointedly non-capitalist creed of creation for creation’s sake — and it is facing massive upheaval in the face of one of the most audacious pieces of enclosure ever attempted in gaming — ongoing as I write.

The threat comes from a formidable company called Valve Corporation, which recently gave modders the option to sell their works via its game download service, Steam.

This is significant because Steam is the most powerful retailing force in PC gaming today, with 125 million active users.

PC games development was in dire straights in the early 2000s. Consoles dominated and seemed to have split the audience, dimming interest in desktop releases. Rampant piracy and lack of consistent support were cited by many firms as putting them off PC development.

However, Valve’s 2003 launch of Steam coincided with and helped stimulate a grassroots recovery by lending confidence to developers and a handy central point for punters to buy games that would have otherwise been difficult to find. Small-scale “indie” developers benefited in particular.

Facilitating what fans are calling a golden age of PC gaming has earned billionaire Valve supremo Gabe Newell a huge amount of goodwill.
But Valve is a business aiming to financially exploit its position, rather than a messianic charity, and it has done so with aplomb — the private company has grown enormously even in the short time since Forbes’s 2012 estimation of Valve’s likely value at £1.65 billion with a mere 330 employees.

And now that it has a near-monopoly position on independent PC game distribution, modding appears to be next.

Valve has already made huge profits by commercialising total mod conversions, from the Half Life series to Team Fortress 2, Dota 2 and Counter-Strike, via its games development wing.

Its original MO was to buy out the concept, hiring lead modders to create follow-up works. If Newell’s new plan works however, Valve won’t even have to do that — it will own the ground they play on.

Always a “mod supportive” firm, Valve dipped into the field in a big way in 2012 by opening Steam Workshop, a one-click system for applying mods to games in its players’ libraries.

Free to use, Workshop made the technically confusing scene much more accessible, connecting modders to a vast new audience.

The longer game of this seeming altruism was to come three years later, and on April 23 Steam launched a scheme to sell mods, rather than to simply give them away.

The announcement has caused a storm of controversy.

On the one hand, there is praise for modders getting an income for their creations. On the other is hostility against both the inherent madness of Steam forcing ownership values on a freewheeling assortment of often anonymous, semi-abandoned or collectively-authored works and Workshop’s astonishingly greedy terms and conditions.

Steam Workshop, the only shop in town, demands not only 75 per cent of a mod’s sale price — which Valve later blamed on a third party — but the right to reuse, repackage and create derivative works.

“Derivative works” is the golden phrase. It means that when a total conversion becomes wildly successful, even if given away initially, Newell will get the sequel.

Appropriation of the next big mod will thus no longer require cash outlays, instead being pre-paid for by Valve’s co-option of the mod community, its evisceration of “creation for creation’s sake.”

By mixing both free and paid-for options with its vast audience, Valve divides the modding populace into “radicals” and “sellers.”

Those who leave current hubs such as nexusmods to set up shop will be missed and those who remain on independent sites suddenly bereft of resources will be pressured towards accepting Newell as king of the ecosystem.

If that shift happens, a Microsoft alumni will have succeeded in enclosing the modding commons and our culture will be poorer for it.

There is resistance, with 60,000 people signing an online petition against Valve’s plan within 48 hours of the announcement.

And, most intriguingly, a number of modders have actively rebelled. On its first day the Workshop, which launched for use with Skyrim, briefly featured an option for high-resolution horse genitals. Still yours for free from Nexusmods — or $99.99 (£65.83) on Workshop.

I for one hope the mods stay gloriously unhinged and may their trains fly without Steam.